The present invention relates to organosilicon block copolymers and methods for making such block copolymers. More particularly, the present invention relates to novel curable polysiloxane block copolymers having at least one block of diorganosiloxane units, at least one block of trifunctional aryl siloxane units, optionally, at least one block of trifunctional alkyl siloxane units, and at least one block of acrylate-functional siloxane units.
Random copolymers, although made from two or more monomers which each have at least one desirable property, do not have properties intermediate the homopolymers. An example would be to copolymerize monomer A which normally gives a hard and brittle film with monomer B which normally gives a soft and flexible film. The object of such copolymerization would be to produce a copolymer having properties intermediate those of homopolymers A and B, for example, to provide a copolymer having a hard but flexible film. With random copolymers it was found that the copolymer would generally be brittle or would still be soft, and the desired intermediate properties would not be obtained. Some improvement might be realized such as the hard and brittle polymer might be more flexible, but only marginally so.
During the past few years a great deal of interest has been shown in "sequential" or "block" copolymers. Although the same monomers and percentages of monomers make up the composition of the random copolymers and the block copolymers, the final polymers in each case differ widely in their properties. Thus, for example, a block copolymer made of monomer A and monomer B may provide the hard but flexible film which was not obtained with the random copolymer.
It would be particularly desirable to obtain UV curable block copolymers which result in transparent, adhesive, tough, dirt repellent and solvent resistant compositions. Until the instant invention such compositions were not available in the art.
Merker, U.S. Pat. No. 2,793,223, discloses acryloxymethylsiloxanes having the formula ##STR1## where R is hydrogen or methyl, R' is a monovalent hydrocarbon radical, and n has a value from 1 to 2 inclusive. Such acryloxy substitued siloxanes can be copolymerized with siloxanes of the unit formula ##STR2## where R" is a monovalent hydrocarbon radical, an acetoxymethyl radical or a halogenated monovalent hydrocarbon radical, and m has an average value from 1 to 3 inclusive. Consideration of the examples reveals that random rather than block copolymers were prepared and that only the toughness of the resulting copolymers is revealed.
Merker, in U.S. Pat. No. 2,922,806, expands upon U.S. Pat. No. 2,793,223 in that the acryloxy or methacryloxy groups are attached to silicon through a divalent alkylene radical having from 2 to 4 carbon atoms. Again, consideration of the examples does not disclose that the resultant polymers or copolymers are adhesive, solvent resistant or dirt repellant.
Merker, U.S. Pat. No. 2,956,044, teaches that acryloxy-functional polymers and copolymers prepared only from organosilicon reactants are closely akin to conventional organosiloxane polymers in their physical properties and hence are useful as molding and impregnating resins, electrical insulating varnishes, water repellent treatments, lubricating fluids, and thermally resistant rubbers and resins. However, by preparing copolymers of acrylate-functional organosilicon units and organic vinylic units, many of the properties of organic vinylic compounds can be imparted to the copolymer, thereby making it useful as a coating agent, impregnating and molding resin, adhesive or bonding agent. Accordingly, the art is taught that adhesion is imparted to UV curable acryloxy-functional polysiloxanes by copolymerizing said polysiloxane with an organic vinylic compound.
Ohto et al., U.S. Pat. No. 3,782,940, discloses photopolymerizable silicones containing at least one unit of the formula ##STR3## where R.sup.1 is hydrogen or an unsubstituted or halogen-substituted phenyl radical, R.sup.2 is hydrogen or a methyl radical, R.sup.3 is an unsubstituted or halogen-substituted divalent hydrocarbon radical having from 1 to 10 carbon atoms, R.sup.4 is an unsubstituted or halogen-substituted monovalent hydrocarbon radical having from 1 to 10 carbon atoms, X is a hydroxyl or alkoxyl radical having from 1 to 4 carbon atoms, a and b are each 0, 1 or 2 with the proviso that a+b=0, 1 or 2, 1 is 0 or 1, and m and n are each 0, 1 or 2 with the proviso m+n=0, 1 or 2.
Ohto et al., U.S. Pat. No. 3,865,588, teaches that the compositions of U.S. Pat. No. 3,782,940 can be used in planographic printing processes in addition to ion-etching processes. Neither of the Ohto et al. patents disclose block copolymers which are transparent, adhesive, tough, dirt repellent and solvent resistant.
Martin, U.S. Pat. No. 3,878,263, describes acrylate functional polysiloxane polymers of the general formula ##STR4## wherein the R's may be the same or different and represent hydrogen or monovalent hydrocarbon radicals having from 1 to 12 carbon atoms, R' is a monovalent hydrocarbon radical, a halogenated monovalent hydrocarbon radical or a cyanoalkyl radical having from 1 to 18 carbon atoms, R" is a divalent hydrocarbon radical having from 1 to 18 carbon atoms or the corresponding divalent hydrocarbon radical having C--O--C linkagkes, R'" is a radical selected from the group consisting of R""O.sub.0.5 and R'.sub.3 SiO.sub.0.5, Z is selected from the group consisting of OR"", R"" and OSiR'.sub.3, a and b equal from 1 to 20,000, c equals from 0 to 3, and e equals from 0 to 2, however, when c is 0 then at least one Z must be OR"". Such polymers are said to be useful as sizing agents and as protective coatings for paper and fabrics.
Baney et al., U.S. Pat. No. 4,035,355, discloses that certain acrylate-containing polyorganosiloxanes and a hydroperoxy polymerization initiator result in an anaerobically curing sealant composition.
The present invention is based on the discovery that UV curable block copolymers having critical amounts of specified siloxane blocks will result in transparent, adhesive, tough, dirt repellent and solvent resistant silicone compositions.